The present invention relates generally to drill bits used in drilling boreholes in the earth, and more particularly to a method and apparatus for fabricating a rotary cone drill bit from multiple drill bit segments.
Various types of rotary drill bits or rock bits may be used to form a borehole in the earth. Examples of such rock bits include roller cone drill bits or rotary cone drill bits used in drilling oil and gas wells. A typical roller cone drill bit includes a bit body with an upper end adapted for connection to a drill string. A plurality of drill bit segments, typically three, is frequently used to form the bit body. Each drill bit segment preferably includes a support arm which extends from a lower end of the bit body. Each support arm also includes a spindle or journal protruding generally radially inward and downward with respect to a projected rotational axis of the bit body. An enlarged generally cylindrical cavity is preferably formed in the bit body to receive drilling fluids from the drill string.
A cutter cone assembly is generally mounted on each spindle and rotatably supported on bearings acting between the spindle and the interior of a cavity or chamber formed within each cutter cone assembly. One or more nozzle housings may be formed on the bit body adjacent to the support arms. A nozzle is typically positioned within each housing to direct drilling fluid passing downwardly from the drill string through the bit body toward the bottom of the borehole being formed. Drilling fluid is generally provided by the drill string to perform several functions including washing away material removed from the bottom of the borehole, cleaning the cutter cone assemblies, and carrying the cuttings radially outward and then upward within an annulus defined between the exterior of the bit body and the wall of the borehole.
Various techniques have previously been used to weld or attach the drill bit segments with each other to form a rotary cone drill bit. U.S. Pat. No. 4,054,772, entitled xe2x80x9cPositioning System for Rock Bit Weldingxe2x80x9d shows apparatus for positioning three drill bit segments relative to each other followed by laser welding to join the drill bit segments with each other to form a bit body with three support arms and respective cutter cone assemblies extending therefrom.
U.S. Pat. No. 3,907,191, entitled xe2x80x9cMethod of Constructing a Rotary Rock Bitxe2x80x9d discloses a method and apparatus for constructing a rotary cone rock bit with an accurate gauge size from multiple drill bit segments. The ""191 Patent discloses xe2x80x9cscissoringxe2x80x9d of drill bit segments relative to each other to establish the desired gauge diameter for the resulting rotary cone drill bit.
U.S. Pat. No. 3,987,859, entitled xe2x80x9cUnitized Rotary Rock Bitxe2x80x9d discloses a method and apparatus for positioning drill bit segments relative to each other to allow an electron beam gun to form a rotary cone drill bit by welding the segments with each other. The ""859 Patent also shows inserting a dowel in adjacent holes in the respective drill bit segments to aid in aligning the drill bit segments with each other prior to welding.
U.S. Pat. No. 4,045,646, entitled xe2x80x9cPositioning Fixture for Rock Bit Weldingxe2x80x9d discloses an apparatus which may be satisfactorily used to position drill bit segments relative to each other and to weld adjacent drill bit segments with each other to form a rotary cone drill bit.
U.S. Pat. No. 4,414,734 entitled xe2x80x9cTriad for Rock Bit Assemblyxe2x80x9d shows a triad which may be positioned in respective holes in three drill bit segments to assist with aligning the drill bit segments with each other prior to welding.
In accordance with teachings of the present invention, disadvantages and problems associated with fabrication and assembly of previous rotary cone drill bits from multiple drill bit segments have been substantially reduced or eliminated. In one aspect of the present invention, three drill bit segments are provided with each drill bit segment having respective mating surfaces that cooperate with each other to allow welding each drill bit segment to adjacent drill bit segments to form a bit body. A generally spherical recess is preferably formed in each drill bit segment. During assembly of the drill bit segments in preparation for welding, a ball is preferably placed in the spherical recess of one drill bit segment. The drill bit segments are then positioned adjacent to each other such that the associated spherical recesses cooperate with each other to form a generally closed spherical cavity to trap the ball therein.
In accordance with teachings of the present invention, multiple drill bit segments are provided with each drill bit segment having a generally irregular, elongated configuration defined in part by an interior surface and an exterior surface. Two mating surfaces are preferably formed on the interior of each drill bit segment with the mating surfaces disposed at an angle of approximately 120xc2x0 relative to each other. The mating surfaces extend from a first end of each drill bit segment to a location intermediate a second end of the respective drill bit segment. A generally spherical recess is preferably formed in the interior surface of each drill bit segment at a junction between the respective mating surfaces intermediate the first end and the second end of the respective drill bit segment.
Technical advantages of the present invention result from placing a ball within generally spherical recesses formed respectively on the interior surface of multiple drill bit segments with each drill bit segment having a spindle or journal with a cutter cone assembly rotatably mounted thereon. The ball and the spherical recesses cooperate with each other to maintain the desired longitudinal spacing of the cutter cone assemblies relative to each other to prevent cone interference while positioning the drill bit segments relative to each other prior to welding. The spherical recesses and the ball cooperate with each other to maintain the desired cone height and the desired gauge diameter of the resulting rotary cone drill bit within acceptable limitations. The ball and spherical recesses also cooperate with each other to establish a pivot point within the interior of the associated drill bit segments to allow adjusting the position of the drill bit segments relative to each other prior to welding while maintaining relative concentric alignment of the drill bit segments relative to each other and a projected axis of rotation for the resulting drill bit. One,result of this generally concentric alignment is maintaining a more uniform wall thickness of an enlarged, generally cylindrical cavity formed in the bit body during threading of the bit body.
Further technical advantages of the present invention include maintaining desired dimensional tolerances of drill bit diameter and location of the cutter cone assemblies relative to the drill bit body even though the dimensions of the drill bit segments used to assemble the resulting drill bit may have less than desired dimensional tolerances. As a result of fabricating rotary cone drill bits from multiple drill bit segments in accordance with teachings of the present invention, the scrap rate for drill bits noncompliance with dimensional tolerances is decreased and the resulting drill bits have improved downhole performance due to enhanced dimensional integrity corresponding with the original design dimensions for the associated rotary cone drill bit. Assembling a rotary cone drill bit in accordance with teachings of the present invention substantially reduces or eliminates variations between originally designed dimensions and the as-built dimensions of the resulting rotary cone drill bit. Teachings of the present invention substantially reduce or eliminate scrap and rework associated with fabricating rotary cone drill bits from multiple drill bit segments.
Other technical advantages of the present invention will be readily apparent to one skilled in the art form the following figures, description, and claims.